(R)—N-(1-(naphthalen-1-yl)ethyl)-3-(3-(trifluoromethyl)phenyl)propan-1-amine has the international non-proprietary name as cinacalcet [CAS number 226456-56-0] and chemical structure as follows:
Cinacalcet is the free base of cinacalcet hydrochloride [CAS Number, 364782-34-3], and the chemical structure of cinacalcet hydrochloride is shown as follows:
It is reported by NPS Pharma. Inc. that cinacalcet hydrochloride (the brand name is Sensipar) is a calcimimetic agent, which is a drug substance that can effectively treat the primary hyperparathyproidism (PHPT). Currently, it has been reported to have the following preparation methods for cinacalcet:(1) Reductive Amination
U.S. Pat. No. 6,211,244 and Drugs of the future (27), 9, 931, 2002, disclose a process to prepare cinacalcet by reductive amination as illustrated below:

However, the method is unsuitable for industrial production due to the toxicity of the reductant sodium cyanoborohydride, the high cost and easy hydrolysis of tetraisopropyl titanate, and unavoidable over-reductive impurities produced in the post-production process, which results in difficult operation, tedious purification and low yield, etc. The over-reductive impurities are difficult to be avoided even by catalytic hydrogenation reduction using heavy metals palladium and platinum as catalysts.
(2) Amide Reduction
Alternatively, WO2007127445 and WO 2008117299 disclose the process as illustrated below:

First, 3-trifluoromethylphenyl propionic acid is used to prepare acyl chloride; then, acyl chloride and (R)-1-naphthyl ethylamine are condensed to obtain amide; finally, carbonyl in amide is reduced to obtain cinacalcet. In the reduction of carbonyl, the reagents used, such as BF3, LiAlH4, or NaBH4/I2, NaBH4/AlCl3 bring difficulties in the operation and cause post treatment problems, so the method is not suitable for scale-up production. Additionally, the process is disfavored for industrial implementation due to the use of hazardous chemicals such as NaBH4/I2, NaBH4/AlCl3, protonic acid, as the large quantity of the chemicals will cause the difficulties of obtaining the high yield as claimed in the articles and too much trouble in work up and purification.
(3) Alkylation
A method of direct alkylation of mesylate (a compound of Formula II, L is methanesulfonate group (OMS)) is published in Chinese Patent No. CN101180261:

In the process, residual (R)-1-(naphthalen-1-yl)ethan-1-amine is not effectively removed from the product because of its similar properties with cinacalcet, as both are alkaline substances. And (R)-1-naphthyl ethylamine is obtained by resolution or asymmetric synthesis, so the cost is high. In order to reduce the cost, the reported synthesis method by direct alkylation uses excessive amount of formula II compound to consume (R)-1-naphthyl ethylamine at maximum, and salify the product by adjusting pH. The unconsumed formula II compound and product could be separated due to the non-salification of excessive formula II compound. But the excessive amount of formula II compound may result in the large amount of dialkylation impurity (Formula IV Compound) present in the final product of alkylation (in the mixtures of end reaction, the content of dialkylation impurity may reach about 7%), while this impurity is an alkaline substance and hard to be separated from cinacalcet. In another aspect, the excessive amount of formula II compound results in the formation of large amount of impurity carbamic acid ester (Formula III Compound), which makes the post treatment of separation and purification more difficult, the yield decreases, and the impurity is difficult to be removed by simply adjusting pH or re-crystallization. See below for formulae II, III, and IV.
Where L is a halogen atom, methanesulfonate group (OMs), p-Toluenesulfonate (OTs), or triflate (OTf).

A Forster-Deker method which is improved from direct alkylation to avoid the by-products of dialkylation, is reported in Org. Process Res. Dev, 2011, 15 (2), P455-461, but due to the solubility problem of intermediate imine, big steric hindrance and little nucleophilicity, the yield may not reach expectation, and the increased steps and operations make the improvement of the method loss outweigh the gain. Similar problems are reported in WO2010004588, such as by the method first forms sulfamide, followed by alkylation and de-protection group, and in WO2010010359, first forms benzylamine, then alkylation and de-benzylation, etc. All these methods are difficult to be industrialized because of the prolongation of steps, difficult group protection and de-protection, abruptly increased environment protection pressure and costs.